<?php
/** 
 * EGP Framework
 *
 * LICENSE
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 * @author     Akon(番茄红了) <aultoale@gmail.com>
 * @copyright  Copyright (c) 2008 (http://www.tblog.com.cn)
 * @license    http://www.gnu.org/licenses/gpl.html     GPL 3
 */

!defined('EGP_LIB_DIR') && die('Access Deny!');

/**
 * XXTEA 算法加密解密类
 *
 * @package    classes
 * @author     hyperjiang <hyperjiang@gmail.com>
 * @copyright  Copyright (c) 2008 (http://www.tblog.com.cn)
 * @license    http://www.gnu.org/licenses/gpl.html     GPL 3
 */
abstract class EGP_Crypt_Xxtea implements EGP_Crypt_Interface
{

    /**
     * Converts long array to string
     *
     * @param  array    $v
     * @param  boolean  $w
     * @return string
     */
    protected static function _long2str($v, $w) {
        $len = count($v);
        $n = ($len - 1) << 2;
        if ($w) {
            $m = $v[$len - 1];
            if (($m < $n - 3) || ($m > $n))
                return false;
            $n = $m;
        }
        $s = array();
        for ($i = 0; $i < $len; $i++)
            $s[$i] = pack("V", $v[$i]);
        return $w ? substr(join('', $s), 0, $n) : join('', $s);
    }

    /**
     * Converts string to long array
     *
     * @param  string  $s
     * @param  boolean $w
     * @return array
     */
    protected static function _str2long($s, $w) {
        $v = unpack("V*", $s . str_repeat("\0", (4 - strlen($s) % 4) & 3));
        $v = array_values($v);
        $w && $v[count($v)] = strlen($s);
        return $v;
    }

    /**
     * Fixes overflow problem
     *
     * @param  integer  $n
     * @return integer
     */
    protected static function _int32($n) {
        while ($n >= 2147483648)
            $n -= 4294967296;
        while ($n <= -2147483649)
            $n += 4294967296;
        return (integer) $n;
    }

    /**
     * shift
     *
     * @return string
     */
    protected static function _shift($e, $k, $p, $y, $z, $sum) {
        return self::_int32((($z >> 5 & 0x07ffffff) ^ $y << 2)
                + (($y >> 3 & 0x1fffffff) ^ $z << 4)) ^ self::_int32(($sum ^ $y)
                + ($k[$p & 3 ^ $e] ^ $z));
    }

    /**
     * Encrypts a plain text
     *
     * @param  string  $str
     * @param  string  $key
     * @return string
     */
    public static function encrypt($str, $key) {
        if ($str == "") {
            return "";
        }
        $v = self::_str2long($str, true);
        $k = self::_str2long($key, false);
        if (count($k) < 4) {
            for ($i = count($k); $i < 4; $i++)
                $k[$i] = 0;
        }
        $n = count($v) - 1;

        $z = $v[$n];
        $y = $v[0];
        $delta = 0x9E3779B9;
        $q = floor(6 + 52 / ($n + 1));
        $sum = 0;
        while (0 < $q--) {
            $sum = self::_int32($sum + $delta);
            $e = $sum >> 2 & 3;
            for ($p = 0; $p < $n; $p++) {
                $y = $v[$p + 1];
                $mx = self::_shift($e, $k, $p, $y, $z, $sum);
                $z = $v[$p] = self::_int32($v[$p] + $mx);
            }
            $y = $v[0];
            $mx = self::_shift($e, $k, $p, $y, $z, $sum);
            $z = $v[$n] = self::_int32($v[$n] + $mx);
        }
        return base64_encode(self::_long2str($v, false));
    }

    /**
     * Decrypts a cipher text
     *
     * @param  string  $str
     * @param  string  $key
     * @return string
     */
    public static function decrypt($str, $key) {
        if ($str == "")
            return "";
        $str = base64_decode($str);
        $v = self::_str2long($str, false);
        $k = self::_str2long($key, false);
        if (count($k) < 4) {
            for ($i = count($k); $i < 4; $i++)
                $k[$i] = 0;
        }
        $n = count($v) - 1;

        $z = $v[$n];
        $y = $v[0];
        $delta = 0x9E3779B9;
        $q = floor(6 + 52 / ($n + 1));
        $sum = self::_int32($q * $delta);
        while ($sum != 0) {
            $e = $sum >> 2 & 3;
            for ($p = $n; $p > 0; $p--) {
                $z = $v[$p - 1];
                $mx = self::_shift($e, $k, $p, $y, $z, $sum);
                $y = $v[$p] = self::_int32($v[$p] - $mx);
            }
            $z = $v[$n];
            $mx = self::_shift($e, $k, $p, $y, $z, $sum);
            $y = $v[0] = self::_int32($v[0] - $mx);
            $sum = self::_int32($sum - $delta);
        }
        return self::_long2str($v, true);
    }

}